Even the remotest hermit knows that the effects of climate change are the greatest threat faced by mankind. So where does that leave artists? Can they contribute anything to debates about the environment? Might the imperatives of environmentalism constrain their freedom to make interesting work? And what do we actually mean when we talk about nature, anyway? Is it polluted oceans or something that occurs closer to home? These are some of the questions answered by Radical Nature, a show with a refreshingly can-do attitude that opens at the Barbican today. Subtitled "art and architecture for a changing planet", it includes land art, installation, video and sculpture ranging from 1969 to the present day.